1. Field of the Invention.
The present invention relates generally to overdrive units for use with automobiles with standard or automatic transmissions and, more specifically, to overdrive transmission units of small size which utilize a planetary gear mechanism in conjunction with clutch packs in order to produce an overdrive transmission unit providing an additional gear ratio for purposes of increasing fuel economy and, in some cases, top speeds of a vehicle. In the past, the use of multiple clutch packs to accomplish the control of the planetary transmission mechanism required a significant amount of axial space within the transmission, as well as a large diameter which, in some circumstances, limited the use of the overdrive transmission unit to specific automobiles, or required modification of an automobile prior to installation.
2. Description of the Prior Art.
In attempts to build a satisfactory overdrive transmission unit, inventors in the past have addressed their efforts to techniques of reducing the amount of space required, techniques to ensure smooth engagement of the gearing, and techniques of timing the change from direct drive to overdrive. While control systems for use with overdrive units have been proposed, most of these systems, have required manual shifting of a lever which either physically controlled an overdrive valve or controlled an electronic circuit which controlled the overdrive valve. Other automatic overdrive units have taught installation of the automatic overdrive unit by rigid connection of its body to the frame of an automobile and installation of the unit mid-range in the drive shaft of the automobile or attachment of the unit to the differential.
None of the prior art of which applicant is aware has taught an automatic overdrive transmission unit which sufficiently reduces both the diameter and the axial space required for installation to make the unit usable, as is the present invention, in the majority of automobiles without modification to the body or frame of the automobile.